In most languages, the concept AND has two different representations. For example, in F# there is logical AND:
let awesome = good && great
Then there is bitwise AND:
// this is pretty common when working with Flags
let hasRed = someColors &&& Color.Red = Color.Red
But then there's VB, for which both concepts use the keyword And. So I implemented a feature in VB to clone an image. I had this code snippet.
Public Shared Function CloneImage(ByVal sourceImage As Bitmap) As Bitmap
If sourceImage.PixelFormat And PixelFormat.Indexed <> 0 Then
Return CreateIndexedImage(sourceImage)
Else
Return CreateNonIndexedImage(sourceImage)
End If
End Function
This code always calls CreateIndexedImage. And it took me a bit to figure out why. It was because the language sees the keyword And as the lowest priority operator and evaluates it last. It does that because it is only considering the priority of logical And. So the actual evaluation was something like (sourceImage.PixelFormat) And (PixelFormat.Indexed <> 0). VB coerces the type of PixelFormat to be truthy, and the second condition will always be true.
The fix was to add parenthesis
If (sourceImage.PixelFormat And PixelFormat.Indexed) <> 0 Then
But this could have been avoided by simply having a different operator between the two uses. Then each could have a different order of precedence.
Top comments (1)
Many languages use
&&for logical and&for bitwiseedit: Totally misread you point, sorry about that :/